Flexible pneumatic duct connectors assembled with internal seals

ABSTRACT

A pair of duct ends are received within opposite ends of a larger diameter housing, each end of the housing being formed with an internal circumferential seal seat groove defined, in part, by an endless radially disposed flange. A continuous radial clearance gap is defined between the outside of each duct end and the radially inner edge of the corresponding flange to accommodate angulation of the duct end. An annular seal assembly is matingly mounted within each of the seal grooves of the housing in a radially compressed preload condition on the outside of the corresponding duct end, the seal assemblies serving to flexibly mount the housing on the two duct ends while preserving the radial clearance gap. Each seal assembly comprises an annular jacket of generally C-shaped radial section enclosing an endless garter spring that biases radially inner and outer walls of the jacket into static sealing contact with the duct end and the housing interior, in the preload condition. The jacket is made of a lubricant impregnated synthetic plastic that is relatively stiff, rather than resilient, having some flexibility, and adapted to withstand high temperatures, that is formed with an annular internal hinge groove so oriented with respect to the flange of the corresponding seal seat groove as to be reinforced thereby, enhancing flexibility of the jacket walls within a wide range of angulation of the duct end relative to the housing. Each of the duct ends mounts a positioning clip, the pair of clips normally limiting axial shifting of the housing to a range preventing disengagement from either of the tube ends, the clips being selectively displaceable to allow sufficient shifting of the housing to give access to the interior thereof for seal inspection and replacement.

United States Patent Schwarz [451 Aug.'1,1972

[54] FLEXIBLE PNEUMATIC DUCT CONNECTORS ASSEMBLED WITH INTERNAL SEALS[72] lnventorz- Steven E. Schwarz, Long Beach,

, Calif.

[73] Assignee: Federal-Mogul Corporation, Detroit,

Mich.

[22] Filed: Aug. 24, 1970 w 211 Appl. No: 66,501

[52] U.S. C1. ..277/153, 277/205, 285/111, 9 285/231 [51] Int. Cl...Fl6j 15/46 [58] Field of Search ..285/1 1 l, 112, 231; 277/26,277/153, 205

[56] References Cited UNITED STATES PATENTS 2,049,801 8/1936 Gage..285/231 2,494,855 1/1950 Anderson ..285/231 2,675,254 4/1954 Davis eta1. ..285/23l 3,512,789 5/1970 Tanner ..277/26 PrimaryExaminer-Robert 1. Smith Attorney-Fulwider, Patton, Rieber, Lee & Utecht[57]- ABSTRACT A pair of duct ends are received within opposite endsbeing formed with an internal circumferential seal seat groove defined,in part, by an endless radially disposed flange. A continuous radialclearance gap is defined between the outside of each duct end and theradially inner edge of the corresponding flange toaccommodate'angulation of the duct end. An annular seal assemblyismatingly mounted within each of the seal groovesof the housing in aradially compressed preload condition on the outside of thecorresponding duct end, the seal assemblies serving to flexibly mountthe housingon the two duct ends while preserving the radial clearancegap. Each seal assembly comprises an annular jacket of generallyC-shaped radial section enclosing an endless garter spring that biasesradially inner and outer walls of thejacket into static sealing contactwith the duct end and the housing interior, in the preload condition.The jacket is made of a lubricant impregnated synthetic plastic that isrelatively stiff, rather than resilient, having some flexibility, andadapted to withstand high temperatures, that is formed with an annularinternal hinge groove so oriented with respect to the flange of thecorresponding seal seat groove as to be reinforced thereby, enhancingflexibility of the jacket walls within a wide range of angulation of theduct end relative to the housing. Each of the duct ends mounts apositioning clip, the pair of clips normally limiting axial shifting ofthe housing to a range preventing disengagement from either of the tubeends, the clips being selectively displaceable to allow sufficientshifting of the housing to give access to the interior thereof for sealinspection and replacement.

of a larger diameter housing, each end of the housing 9 Claims, 6Drawing Figures 40 if v 3 11w 1 59 .:'.i 3/ 2 i l/11 23 [1 1111 27 .10

FLEXIBLE PNEUMATIC DUCT CONNECTORS AS SEMBLED WITH INTERNAL SEALSBACKGROUND OF THE INVENTION The present invention relates to an improvedflexible internally sealed duct connector assembly for use in hot gaspiping systems, such as jet aircraft, to compensate for installationmisalignment and to absorb thermal movement in the system. y

In ducting systems for hot gases at high pressures it is essential toprovide a means to interconnect adjacent duct ends in a manner toprevent leakage of the got gases. Typically, the pair of duct ends to bejoined are misaligned, rather than aligned, usually being axially offsetand/or having their axes angularly related rather than parallel.Accordingly, the duct connector must be capable of accommodating variousdegrees of angular relationship to the duct ends to be joined while, atthe same. time, providing a sealing means that is reliable throughoutthe possible range of angulation. The

problem of providing a satisfactory seal to accommodate this angulationis further compounded by the fact that the .sealing means employed mustalso be capable .of providing a static seal, a negative pressure seal,and must accommodate'relative axial and/or rotational movements of theparts. Additionally, since the duct connector must receive the adjacenttube ends through opposite ends with sufficient clearance to accommodateangular misalignment, the clearance gaps tend to induce undesirableextrusion of the seal ring material employed, particularly at the veryhigh pressures and temperatures to which the connector is subjected.While seal ring materials which will satisfactorily withstand the. highpressures and temperatures involved have been available, it has. been aproblem to adapt such materials to duct connectors involving angularmisalignment particularly with regard to the prevention of extrusion ofthe seal material through the clearance gaps.

SUMMARY OF THE INVENTION In general, the duct connector of thisinvention comprises a tubular housing that is internally formed atopposite ends with seal seat grooves, each groove holding a radiallycompressed spring-loaded gland or jacket that sealingly embraces one ofa pair of tube ends. Positioning clips are carried on the tube ends,defining a pair of opposed stops to limit the range of axial shiftingofthe housing on the tube ends.

The seal seat grooves are integrally formed parts of the housing, eachdefined, in part, by a radially inwardly directed flange, the inneredges of the flanges defining the least diameter of the housing. Eachgroove is asymmetrical with respect to its median diametral plane,developing or necking onthe side away from the flange into afrusto-conical tapered portion narrowing toward the center of thehousing. The mid-portion of the housing is of a larger diameter than thehousing ends. The arrangement is such that each tube end and thecorresponding end flange of the housing are radially spaced apart toprovide a clearance gap for angulating'the tube end, the larger diameterportion of the housing similarly providing clearance for the inner endof the tube. The tube ends are flexibly interconnected to the oppositeends of the housing by means of a pair of sealing assemblies, each ofwhich is mounted within one of the seal seat grooves of the housing.

Each seal assembly comprises an annular jacket containing a garterspring. The jacket is preferably made of a graphite-filled Teflon"material having a generally C-shaped radial cross section whose openingfaces axially of the jacket. The garter spring is preferably formed froman elongate strip of flat ribbon-like spring material, for example,stainless steel, or other heat resistant spring material, that ishelically coiled with opposite ends of the strip being joined to definea circular length to fit within the jacket. The jacket internallydefines a pocket of circular cross section to matingly receive thegarter spring, the pocket diameter being the same as the normalunstressed radial diameter included by the turns of the garter springband. With this arrange ment, the garter spring, when in the jacketpocket, resiliently opposes radial compression of the seal assembly.

The unstressed inner diameter of the seal assembly, (including thegarter spring), is such as to define an interference fit with the outersurface of the tube end to be received therein. The outer diameter ofthe unstressed seal assembly is formed, in part, with a cross sectionalconfiguration adapted for mating reception within a seal seat groove ofthe housing end, with a close sliding or slight interference fit.Accordingly, when the seal assembly is in place, its spring is deformedalong with the jacket, the' radial compression producing a sealingengagement.

The jacket is formed with a radially flat face on the outside of thewall in opposition to the opening into the jacket, adapted for flatregistration with the radial flange of the seal seat groove. This wallis relatively thick and, due to the nature of the material of whichmade, is stiff. In order to increase flexibility of the radially innerand outer sidewalls of the jacket, the circular cavity is formed with acircular flexure notch in opposition to the radial flange and radiallyoutwardly beyond the inner edge of the flange. With this arrangement,sufficient flexibility is induced in the jacket to permit its radialcompression and angulation of the tube end. At the same time sufficientjacket wall thickness is retained in opposition to the clearance gap toprevent extrusion of the material under very high temperatures andpressures. Further, the inside seal profile is a developed curvatureadapted to accept all degrees of tube angulation while maintaining itssealing effectiveness on the tube end.

' BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view ofa duct connector assembly incorporating the invention.

FIG. 1a is a view, on an enlarged scale, taken along the line la-la FIG.1, showing details of construction of the positioning clip.

FIG. 2 is a broken diametral section, on a larger scale, through aninterconnecting assembly of a tube end, seal assembly and one end of thehousing.

FIG. 3 is a radial cross-sectional view of the seal assembly in theunstressed condition.

FIG. 4 is a half sectional view similar to FIG. 2, but with the tube endoriented coaxially with the housing.

FIG. 5 is a partial elevational view, in the direction of the arrow 5 ofFIG. 3, with a portion of the jacket cut away.

DESCRIPTION OF THE PREFERRED EMBODIMENT The duct connector assemblycomprises a pair of tube ends 10 within opposite ends of the housing 11,the latter at opposite ends internally mounting a pair of sealassemblies 12 within which the pair of tube ends are mounted. Each ofthe tube ends 10 mounts a positioning means 13 to limit axial movementof the housing 11 relative to the tube ends. It will be understood thatthe tube ends 10 are rigidly interconnected to sections of other tubingof a hot gas piping system whereby the tube ends 10 are, in effect,fixed or restrained against movement. The housing 11, however, isunrestrained except for its frictional engagement with the innersurfaces of the pair of seal assemblies 12 and, accordingly, isrotatable and axially shiftable with respect to the tube ends.

While an exaggerated degree of angularity of one of the tube ends 10 isillustrated in FIG. 1, in the preferred embodiment the assembly isintended to normally accommodate angular misalignment of say on theorder of between and 7. It should further be noted that the arrangementin FIG. 1 indicates a condition in which the axes of the two tube ends10, though angularly related, do intersect. However, the invention mayalso be employed in situations in which the tube ends have their axesparallel and offset from one another or they may have angularly relatedaxes which do not intersect.

Each of the positioning clip means 13 comprises a bracket strap 14 ofhat-shaped profile, disposed circumferentially of the tube end 10,having the bottom flanges thereof secured to the tube end, as by meansof spot welds 15. An abutment clip 16 which may be formed of a wire rodmaterial, has one end pivotally secured, as at 17, to the radiallyprojecting legs of the bracket 14, the free end of the clip being bentradially inwardly, as indicated at 18, to serve as an abutment to limitaxial displacement of the housing 11 by contact with an adjacent end ofthe housing. A pair of coil springs 19 each has its opposite endsinterconnected to the pair of radially projecting legs of the bracket14, the pair of springs being under tension and looped over the clip 16to normally bias the clip into the full line position illustrated inFIG. 1.

The duct ends 10 being fixedly mounted in place, the arrangement of thepositioning clip means 13 is such that the span between the abutmentportions 18 thereof exceeds the overall length of the housing 11 mountedon the duct ends. Accordingly, in their normal position the abutmentportions 18 of the pair of positioning clips positively limit the extentto which the housing 11 can be displaced relative to the duct ends. Whenit is desired to gain access to the interior of either end of thehousing 11, for purposes of seal inspection or replacement, either oneof the clips 16 may be raised, as indicated by the dotted line positionin FIG. 1. Thereafter, the housing 11 may be shifted axially on one ofthe duct ends to be withdrawn from the other of the duct ends 10, afterwhich one end of the housing is open permitting retrieval of thecorresponding end seal assembly for inspection.

At both ends, the housing 11 is integrally formed with an internal sealseat groove that is defined, in part, by an endless radially inwardlydirected flange 21, terminating in a radially innermost edge 22 ofpredetermined diameter. The relationship of the inner edge 22 of theflange 21 to the outer diameter of the tube 10 is such as to define acircumferential clearance gap 23, whose radial dimension is selected topermit the desired degree of freedom of angulation of the tube endrelative to the housing 1 1. BY the same token, the mid portion of thehousing 11 is enlarged to be of sufficient internal diameter toaccommodate the maximum angulation of the tube end which is to bepermitted.

By reference to FIG. 2 it will be seen that when a tube end is angularlyrelated to the housing 11 that the clearance gap 23 is greatly enlargedat one side and diminished at the opposite side. Thus, at the upper endof FIG. 2 the gas 23 is on the order of double the magniture of theradial clearance between the flange edge 22 and the outside of the tube10 in the lower half of the figure. Thus, the gap condition, essentialto permit angulation, at the same time creates a dangerous conditionthat is especially conductive to extrusion of the seal material throughthe enlarged portion of the gap.

Each seal assembly 12 comprises an annular jacket 24 that encases anendless garter spring 25. As is shown in FIG. 3, the jacket 24 isgenerally C-shaped in radial cross-section, comprising a radially outerlip 26 and radially inner lip 27 joined together by a radial wallportion 28.

Internally, the wall portions of the jacket 24 define an endless pocket30 which, in radial section, comprises a major portion of a circlecommunicating with an axially facing opening 31 of the jacket. Thegarter spring 25 is formed from a flat strip of ribbon-like heatresistant spring material, for example stainless steel. As is best seenin FIG. 5, the ribbon of metal is helically wound and, preferably, hasits opposite ends permanently joined to define a garter of the same meandiameter as the mean diameter of the pocket 30 which is to receive theribbon, or approximately so. Preferably, the radial diameter included byloops of the ribbon is the same, approximately, as the diameter of thecircular section portion of the pocket 30. Although the width of theopening 31 into the jacket pocket 30 is narrower than the radial widthof the garter spring 25, the coils of the spring can be sufficientlyradially compressed to pass through the opening 31 to be seated in thepocket 30. Preferably, the proportions are such that the pocketed garterspring 25 is substantially relaxed within its pocket, with a closesliding fit or a snug fit, although the tolerances in this regard arenot crucial.

The jacket 24 may be molded, extruded or machined to the desired shapefrom a synthetic resin that is though, durable and adapted to withstandhigh temperatures, having a low coefiicient of friction and with somedegree of flexibility. The preferred material is thepolytetrafluoroethylene resin known as Teflon. In order to furtherdecrease the coefficient of friction and thus facilitate assembly of theparts, it is preferred that the resin material be impregnated with asuitable lubricant, such as graphite.

Preferably, each seal seat groove of the housing 11 is adapted to seatits seal assembly 12 in a manner to retain it against axialdisplacement, as well as to accomplish effective sealing action of theradially outer lip 26 against the inner surface of the groove.Accordingly, inwardly of the flange 21, each groove. develops into asubstantially cylindrical section 35 and then into a necked down,substantially frusto-conical section 36.

The outer surface of the outer lip 26 of the jacket 24 iscorrespondingly shaped with a cylindrical portion 37 and a taperedsection 38, which profile mates with the corresponding portions of thegroove profile. The radial wall portion 28 of the jacket 25 has a flatradial surface 39 adapted for flat abutment with the inside face of theradial flange 21. A chamfer 40 may be defined at the intersection ofsurfaces 39 and 37 of the jacket to provide clearance to insure firmflat engagement of the jacket surface 39 against the flange 21 and ofthe jacket surface 37 against the groove portion 35.

The inner lip 27 of the jacket 24 is formed in radial section with aprofile adapted to increase the wall thickness of the lip 27 at itsjunction with the radial wall 28 of the jacket. This profile, forexample, may be a curve of constant radius R, as shown in FIG. 3, havingits center within a diametral plane including the center of the pocket30, radially outwardly of the center of the pocket 30, and of alength'atleast sufficient to produce a profile of the inner surface 42 adapted tointersect the flat radial wall 39 adjacent the radially inner edge 22 ofthe flange 21. At the same time, the least diameter defined by thesurface 42 is smaller than the outer diameter of the tube end to bemounted therewithin.

It is essential that the radial thickness of the jacket assembly 24 besuch that the jacket is radially compressed when seated within itsgroove while mounting a tube end 10 therein. Thus, comparing FIGS. 3 and4 it will be seen that the radial thickness of the sea] assembly 24 hasbeen substantially lessened and, in this preload condition, may becompressed on the order of 10 to percent. However, the syntheticmaterials employed are not, typically, sufficiently resiliently compressable or flexible to achieve this or any satisfactory degree ofradial compression in order to preload the seal and, also, maintain asufficient wall thickness of the seal material to prevent extrusionunder high pressures and temperatures while mounting an angularlyrelated duct end 10 therewithin. To overcome these disadvantages of theseal materiaL-successfully, a flexure notch is formed in the pocket 30ofthe inner surface of the radial wall 28 of the jacket 24, theflexurenotch 44 defining an endless circle. The notch 44 is disposed at leastradially outwardly beyond the radially inner edge 22 of the flange 21,and, preferably, radially outwardly beyond the center of the pocket 30.Notch 44 has a depth, in the axial direction as viewed in FIG. 3, forexample, of no more than half the thickness of the jacket wall 28 atthat position. The wall-portion 28 is, accordingly somewhat thinned andweakened but, by virtue of its being reinforced by the flange 21,nevertheless provides a satisfactory hinge for flexing of theradiallyinner lip 27 of the jacket.

In FIG. 4, the tube end 10 is positioned coaxially with the housing 11and, accordingly, the seal assembly 12 is radially compressed in adiametral plane and the garter spring and its pocket are slightlydeformed, in radial section, to a somewhat ovoid or ellipticalconfiguration. AT the same time, that portion of the inner lip 27 incontact with the outer surface of the tube end 10 is slightly compressedand slightly flattened. The degree of compression or distortion of thespring and its pocket and the degree of the flattening of the sealinglip 27 are exaggerated in FIG. 4 (as well as in FIG. 2) in order toillustrate the sealing action which occurs, as is also the degree ofdeformation of the flexure notch 24. However, assuming an unpressurizedcondition of the ducting system, an effective seal is neverthelessprovided since the'coils of the spring 25 react throughout 360 toforcefully bias all outer surfaces of the jacket 24 against theconfronting surfaces of -'the seal seat grooveand the duct end 10. Underconditions of internal pressure, the sealing action increasesproportionately with increase in pressure due to the presence ofpressurized gas within the pocket of the jacket 24.

Ordinarily, a tube end 10 would not be angularly ofiset more than 7 withrespect to the housing 11. However, FIG. 2 represents an extreme angularoffset, on the order of 10, which can actually be accommodated withsmaller diameters of tubing. The extreme condition of FIG. 2 is shown,in order to particularly illustrate the manner in which the ductconnector assembly provides a successful internal seal under conditionsof angular misalignment of tube ends. While the gap 23 in the lower halfof the drawing has been decreased it will be noted that the gap, in itsdiametrically opposite portion in the upper half of the drawing, is verygreatly enlarged. HOwever, due to the presence of the flexure notch 44and the profile given to the radially inner surface 42 of inner lip 27,the jacket is enabled to be radically flexibly deformed while at thesame time maintaining an adequate seal wall thickness to preventextrusion of the seal material through the gap 23.

As examination of FIG. 2 will show, the jacket lower lip surface 42 hasa substantially elliptical line or path of sealing engagement around theduct end 10. Accordingly, the angle of the lip 27 relative to the axisof the housing 11 changes constantly, circularly of the lip, asillustrated by the two different lip angles at opposite ends of themajor axis of the ellipse, shown in FIG. 2. From this, it will beappreciated that the lip profile 42 and the flexure groove 44 arecritically important to successful scaling in this environment.

The duct construction of this invention is also extremely well suited tomaintain the integrity of the internal seals under conditions ofnegative pressure. Due to the mating configuration of the radiallyoutermost surfaces of the outer lip 26 of the jacket and the innersurfaces of the seal seat groove, the jacket 24 is successfully heldagainst axial displacement in the groove. Since the sloping portion 36of the groove provides a wedging action relative to the outer surface ofthe duct end 10 preventing axially inward movement of the jacket and,also, provides a surface against which the spring 25 reacts, the innerlip 27 is kept sealingly engaged with the outside surface of the ductend 10 at conditions of negative pressure. Due to the wedging ac tion,as amplified by the negative pressure and the spring reaction, thisresult is attained and abetted by the presence of the flexure notch 44.

While the presently preferred embodiment of the invention has beendescribed in considerable specific structural detail, it will beunderstood that the invention is susceptible to various changes andmodifications within the purview of one skilled in the art.

I claim:

1. In a flexible pneumatic hot gas duct connector, the improvementcomprising:

a housing with an end formed with a circumferential internal seal seatgroove including a radially inwardly directed flange;

a duct end within said flange, of smaller external diameter than thediameter of the inner edge of said flange, to define a clearance gap forangular misalignment of the axis of said duct and of said housing;

an annular jacket of an essentially inelastic, relatively stiff, heatresistant synthetic plastic material formed with a radially outer wallwith an outer surface adapted for seating within said groove of saidhousing end;

said jacket having a radially disposed wall adapted for flat engagementwith the inside of said flange;

said jacket having a radially inner wall with a radially inner surfaceadapted for a sealing interference fit on the outside of said duct endwhereby to interconnect said duct end to said housing;

said walls of said jacket defining an internal annular pocket with anendless opening facing axially inwardly of said housing for pressurefluid communication with gases in said housing; and

said radially disposed wall of said jacket on the internal face thereof,within said pocket, being formed with an annular groove, of smallerradial cross-sectional area than the radial cross-sectional area of saidpocket, in opposition to said flange for defining an endless relativelythin hinge portion of said radially disposed wall about which said innerand outer walls are flexibly biased, in response to fluid pressuresinternally of said jacket, into tighter sealing engagement with saidduct end and said groove, respectively, and said inner wall is flexed todifferent degrees circularly around said jacket in response to angularmisalignment of said duct end and said housing.

2. A flexible duct connector as in claim 1 in which said radially innerwall of said jacket increases in wall thickness toward said radiallydisposed wall in order to reinforce said inner wall against extrusionthrough said gap by the pressure of the gas.

3. A flexible duct connector as in claim 1 in which:

said internal annular pocket is adapted to retain a spring means; and

a circularly arranged spring means is disposed within said pocket forresiliently opposing compression radially across said inner and outerwalls of said jacket;

said spring means and said pocket being keyed together against relativeaxial displacement.

4. A flexible duct connector as in claim 3 in which:

said pocket normally is partially of circular radial cross-section, inthe unstressed condition; and

said spring means comprises an endless spring made of helically coiledflat ribbon whose coils define a radial diameter of said spring adaptedfor nesting engagement in said pocket;

said pocket and the coils of said spring being radially compressed whenengaged on said duct end;

said flexure groove being positioned radially outwardly beyond said edgeof said flange and opening into said pocket. 5. A flexible ductconnector as in claim 4 in which: the inner surface of said housinggroove and the outer surface of said outer lip of said jacket havemating profiles adapted to key said jacket against a a1 d' 1 cc tinwardlof said housin profil inclii iiig a portion converging towards said ductend and inwardly of said housing to wedgingly resist said axialdisplacement;

the convergent portion of said housing providing a rigid surface againstwhich coils of said spring react to maintain said radially inner surfaceof said radially inner wall in sealing engagement with said duct andagainst a negative pressure condition.

6. A flexibly adjustable seal assembly for interconnecting a duct end toa housing with'clearance to accommodate misalignment therebetween,comprising:

an annular jacket of a relatively stiff, heat resistant,

synthetic plastic material having an annular pocket communicating withan axially opening entrance to said pocket;

said pocket, in radial section and in an unstressed condition of saidjacket, being of a circular crosssection subtending the major part of acircle;

said jacket having aradial wall on the side thereof opposite said pocketentrance formed with an annular radial flat outer surface; and

a circularly arranged spring means extending circularly throughout saidpocket, said spring means being formed of coils of a flat springmaterial, said coils defining a normal unstressed diameter adapted formating engagement with the circular section of said pocket to be heldagainst axial displacement;

said pocket being formed with an annular groove at the interior surfaceof said radial wall located radially outwardly relative to a radiallyinner edge of said flat outer surface of said radial wall;

said jacket having a radially inner wall with a radially inner sealingsurface, said groove defining a circular hinge about which said innerwall is flexible to varying degrees when said jacket is radiallycompressed by an angularly misaligned duct end.

7. A flexibly adjustable seal assembly as in claim 6 in which saidsealing surface of said inner wall is formed with cross-sectionalprofile providing an increasing wall thickness, relative to said pocket,from the least diameter of said sealing surface to said sealing surfacesjunction with said flat outer surface of said radial wall.

8. A flexibly adjusting seal assembly as in claim 7 in which saidsealing surface, in the unstressed condition of said jacket, has thecross-sectional profile of a curve of constant radius that intersectssaid radially inner edge of said flat surface of said radial wall.

9. A flexibly adjusting seal assembly as in claim 6 in which saidannular groove is located radially outwardly relative to the geometriccenter of said circular crosssection of said pocket.

1. In a flexible pneumatic hot gas duct connector, the improvementcomprising: a housing with an end formed with a circumferential internalseal seat groove including a radially inwardly directed flange; a ductend within said flange, of smaller external diameter than the diameterof the inner edge of said flange, to define a clearance gap for angularmisalignment of the axis of said duct and of said housing; an annularjacket of an essentially inelastic, relatively stiff, heat resistantsynthetic plastic material formed with a radially outer wall with anouter surface adapted for seating within said groove of said housingend; said jacket having a radially disposed wall adapted for flatengagement with the inside of said flange; said jacket having a radiallyinner wall with a radially inner surface adapted for a sealinginterference fit on the outside of said duct end whereby to interconnectsaid duct end to said housing; said walls of said jacket defining aninternal annular pocket with an endless opening facing axially inwardlyof said housing for pressure fluid communication with gases in saidhousing; and said radially disposed wall of said jacket on the internalface thereof, within said pocket, being formed With an annular groove,of smaller radial cross-sectional area than the radial cross-sectionalarea of said pocket, in opposition to said flange for defining anendless relatively thin hinge portion of said radially disposed wallabout which said inner and outer walls are flexibly biased, in responseto fluid pressures internally of said jacket, into tighter sealingengagement with said duct end and said groove, respectively, and saidinner wall is flexed to different degrees circularly around said jacketin response to angular misalignment of said duct end and said housing.2. A flexible duct connector as in claim 1 in which said radially innerwall of said jacket increases in wall thickness toward said radiallydisposed wall in order to reinforce said inner wall against extrusionthrough said gap by the pressure of the gas.
 3. A flexible ductconnector as in claim 1 in which: said internal annular pocket isadapted to retain a spring means; and a circularly arranged spring meansis disposed within said pocket for resiliently opposing compressionradially across said inner and outer walls of said jacket; said springmeans and said pocket being keyed together against relative axialdisplacement.
 4. A flexible duct connector as in claim 3 in which: saidpocket normally is partially of circular radial cross-section, in theunstressed condition; and said spring means comprises an endless springmade of helically coiled flat ribbon whose coils define a radialdiameter of said spring adapted for nesting engagement in said pocket;said pocket and the coils of said spring being radially compressed whenengaged on said duct end; said flexure groove being positioned radiallyoutwardly beyond said edge of said flange and opening into said pocket.5. A flexible duct connector as in claim 4 in which: the inner surfaceof said housing groove and the outer surface of said outer lip of saidjacket have mating profiles adapted to key said jacket against axialdisplacement inwardly of said housing; said profile including a portionconverging towards said duct end and inwardly of said housing towedgingly resist said axial displacement; the convergent portion of saidhousing providing a rigid surface against which coils of said springreact to maintain said radially inner surface of said radially innerwall in sealing engagement with said duct and against a negativepressure condition.
 6. A flexibly adjustable seal assembly forinterconnecting a duct end to a housing with clearance to accommodatemisalignment therebetween, comprising: an annular jacket of a relativelystiff, heat resistant, synthetic plastic material having an annularpocket communicating with an axially opening entrance to said pocket;said pocket, in radial section and in an unstressed condition of saidjacket, being of a circular cross-section subtending the major part of acircle; said jacket having a radial wall on the side thereof oppositesaid pocket entrance formed with an annular radial flat outer surface;and a circularly arranged spring means extending circularly throughoutsaid pocket, said spring means being formed of coils of a flat springmaterial, said coils defining a normal unstressed diameter adapted formating engagement with the circular section of said pocket to be heldagainst axial displacement; said pocket being formed with an annulargroove at the interior surface of said radial wall located radiallyoutwardly relative to a radially inner edge of said flat outer surfaceof said radial wall; said jacket having a radially inner wall with aradially inner sealing surface, said groove defining a circular hingeabout which said inner wall is flexible to varying degrees when saidjacket is radially compressed by an angularly misaligned duct end.
 7. Aflexibly adjustable seal assembly as in claim 6 in which said sealingsurface of said inner wall is formed with cross-sectional profileproviding an increasing wall thickness, relative to said pocket, fromthe least diameter of said sealing surface to said sealing surface''sjunction with said flat outer surface of said radial wall.
 8. A flexiblyadjusting seal assembly as in claim 7 in which said sealing surface, inthe unstressed condition of said jacket, has the cross-sectional profileof a curve of constant radius that intersects said radially inner edgeof said flat surface of said radial wall.
 9. A flexibly adjusting sealassembly as in claim 6 in which said annular groove is located radiallyoutwardly relative to the geometric center of said circularcross-section of said pocket.